Alternative source module array characterization

ABSTRACT

A system and method for mapping relative positions of a plurality of alternative energy source modules. In one embodiment, the method includes injecting a first contribution current into a power grid by a first alternative energy source module of the plurality of alternative energy source modules and determining an output voltage for each of the plurality of alternative energy source modules. The method also includes constructing a data structure of the relative positions of the plurality of alternative energy source modules employing the output voltage for ones of the plurality of alternative energy source modules.

This application claims the benefit of U.S. Provisional Application Ser.No. 62/002,885 entitled “Inverter Array Characterization,” filed May 25,2014, which is incorporated herein by reference.

BACKGROUND

Power inverters convert a direct current (“DC”) power to an alternatingcurrent (“AC”) power. For example, some power inverters are configuredto convert the DC power to an AC power suitable for supplying energy toan AC grid and, in some cases, an AC load coupled to the AC grid. Oneparticular application for such power inverters is the conversion of DCpower generated by an alternative energy source, such as photovoltaiccells (“PV cells” or “solar cells”), fuel cells, DC wind turbines, DCwater turbines, and other DC power sources, to single-phase AC power fordelivery to an AC grid at a grid frequency.

In an effort to increase the amount of AC power generated, a largenumber of power inverters may be used in a particular application. Insome implementations, each power inverter is incorporated or otherwiseassociated with an alternative energy source to form an alternativeenergy source module. Such modules are typically located in remote orotherwise difficult to reach locations (e.g., a solar cell panel locatedon a roof).

A particular kind of an alternative energy source module is known as analternating current photovoltaic (“ACPV”) module. An ACPV moduleincludes at least a solar module (that produces DC power in response tosunlight), and an inverter that converts the DC power from the solarmodule to power grid compatible AC power. Such an inverter may be knownas a microinverter.

When an array of at least two ACPV modules is installed on a roof, thearray may be difficult to access at a later date for purposes of repair,maintenance, or augmentation of the array. An identifying mark, such asa serial number, will normally be associated with each ACPV module. Oncethe array has been installed, the identifying marks will generally notbe visible or easily accessible.

BRIEF DESCRIPTION OF THE DRAWINGS

The concepts described herein are illustrated by way of example and notby way of limitation in the accompanying FIGUREs. For simplicity andclarity of illustration, elements illustrated in the FIGUREs are notnecessarily drawn to scale. Where considered appropriate, referencelabels have been repeated among the FIGUREs to indicate corresponding oranalogous elements.

FIG. 1 illustrates a simplified block diagram of an embodiment of asystem for generating alternative energy;

FIG. 2 illustrates a simplified block diagram of an embodiment of theinverter of the system of FIG. 1;

FIGS. 3 and 4 illustrate simplified circuit diagrams of an embodiment ofthe inverter circuit of FIG. 2;

FIG. 5 illustrates a simplified block diagram of an embodiment of theinverter controller of the inverter of FIG. 2;

FIG. 6 illustrates a simplified block diagram of an embodiment of abranch circuit including a plurality of alternative energy sourcemodules;

FIG. 7 illustrates a graphical representation of an embodiment of adistribution of the terminal voltages in the branch circuit of FIG. 6;

FIGS. 8 and 9 illustrate simplified flow diagrams of embodiments ofmethods for mapping relative positions of a plurality of alternativeenergy source modules; and

FIG. 10 illustrates a simplified block diagram of an embodiment of aplurality of branch circuits forming a multi-branch array.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and will be describedherein in detail. It should be understood, however, that there is nointent to limit the concepts of the present disclosure to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives consistent with the presentdisclosure and the appended claims.

References in the specification to “one embodiment,” “an embodiment,”“an illustrative embodiment,” etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may or may not necessarily includethat particular feature, structure, or characteristic. Moreover, suchphrases are not necessarily referring to the same embodiment. Further,when a particular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to engage such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

The disclosed embodiments may be implemented, in some cases, inhardware, firmware, software, or any combination thereof. The disclosedembodiments may also be implemented as instructions carried by or storedon a transitory or non-transitory machine-readable (e.g.,computer-readable) storage medium, which may be read and executed by oneor more processors. A machine-readable storage medium may be embodied asany storage device, mechanism, or other physical structure for storingor transmitting information in a form readable by a machine (e.g., avolatile or non-volatile memory, a media disc, or other media device).

In the drawings, some structural or method features may be shown inspecific arrangements and/or orderings. However, it should beappreciated that such specific arrangements and/or orderings may not berequired. Rather, in some embodiments, such features may be arranged ina different manner and/or order than shown in the illustrative FIGUREs.Additionally, the inclusion of a structural or method feature in aparticular FIGURE is not meant to imply that such feature is required inall embodiments and, in some embodiments, may not be included or may becombined with other features.

Turning now to FIG. 1, illustrated is a simplified block diagram of anembodiment of a system 100 for generating alternative energy. The system100 may include an array 102 of alternative energy source modules(designated “ACPV module”) 104 and an inverter array gateway 112electrically coupled to each of the alternative energy source modules104 via a conductor such as an alternating current (“AC”) power linecable 108. The alternative energy source modules 104 may be configuredto convert direct current (“DC”) power from an alternative energy source(e.g., a photovoltaic module) to AC power, which is supplied to a powergrid via a service panel 110 via the AC power line cable 108. In theillustrative embodiment, the alternative energy source modules 104 areembodied as photovoltaic modules configured to convert solar energy toAC power. However, in other embodiments, other types of alternativeenergy sources may be used such as, for example, fuel cells, DC windturbines, DC water turbines, and/or other alternative energy sources.Additionally, although the illustrative array 102 includes twoalternative energy source modules 104, the array 102 may include more orfewer alternative energy source modules 104 in other embodiments.

The illustrative system 100 also includes the inverter array gateway112, which provides a communication portal to the array 102. In use,each of the alternative energy source modules 104 is configured tocommunicate with the inverter array gateway 112 and/or other devices viathe inverter array gateway 112. To do so, as discussed in more detailbelow, the alternative energy source modules 104 may modulateinformation to be transmitted on to an output waveform, which may be anAC waveform, generated by each alternative energy source module 104.Such modulation may include modulating information on to a modulationsignal and/or a carrier signal of the output waveform as discussedbelow. It should be appreciated that because the output waveform of thealternative energy source modules 104 is used for such communications,additional communication circuitry (e.g., a power line carriercommunication circuit) is not required in the alternative energy sourcemodules 104.

As discussed above, in the illustrative embodiment, the alternativeenergy source modules 104 may be embodied as photovoltaic modulescoupled to or including solar panels. As such, each of the alternativeenergy source modules 104 may include a DC photovoltaic module(designated “DC PV module”) 120 and an inverter 122. The DC photovoltaicmodule 120 may be embodied as one or more photovoltaic cells and isconfigured to deliver DC power to the inverter 122 in response toreceiving an amount of sunlight. Of course, the DC power delivered bythe DC photovoltaic module 120 is a function of environmental variablessuch as, without limitation, sunlight intensity, sunlight angle ofincidence and temperature. The inverter 122 is configured to convert theDC power generated by the DC photovoltaic module 120 to AC power. Insome embodiments, the inverter 122 and the DC photovoltaic module 120are located in a common housing. Alternatively, the inverter 122 mayinclude its own housing secured to the housing of the DC photovoltaicmodule 120. Additionally, in some embodiments, the inverter 122 isseparate from the housing of the DC photovoltaic module 120, but locatednearby.

Each of the illustrative inverters 122 may include a DC-to-AC invertercircuit (designated “inverter circuit”) 124 and an inverter controller126. The DC-to-AC inverter circuit 124 may be configured to convert theDC power generated by the DC photovoltaic module 120 to AC power at thepower grid frequency. The operation of the inverter 122 may becontrolled and monitored by the inverter controller 126. Theillustrative inverter controller 126 includes a processor 130 and amemory 132. Additionally, the inverter controller 126 may include otherdevices commonly found in controllers which are not illustrated in FIG.1 for clarity of description. Such additional devices may include, forexample, peripheral devices, data storage devices, input/output ports,and/or other devices.

The processor 130 of the inverter controller 126 may be embodied as anytype of processor capable of performing the functions described hereinincluding, but not limited to, a microprocessor, digital signalprocessor, microcontroller, or the like. The processor 130 isillustratively embodied as a single core processor, but may be embodiedas a multi-core processor having multiple processor cores in otherembodiments. Additionally, the inverter controller 126 may includeadditional processors having one or more processor cores in otherembodiments.

The memory 132 of the inverter controller 126 may be embodied as one ormore memory devices or data storage locations including, for example,dynamic random access memory devices (“DRAM”), synchronous dynamicrandom access memory devices (“SDRAM”), double-data rate synchronousdynamic random access memory device (“DDR SDRAM”), flash memory devices,and/or other volatile memory devices. The memory 132 is communicativelycoupled to the processor 130 via a number of signal paths, such as adata bus, point-to-point connections, or other interconnects. Althoughonly a single memory 132 is illustrated in FIG. 1, in other embodiments,the inverter controller 126 may include additional memory.

The inverter array gateway 112 may include a demodulation circuit 150configured to demodulate the information transmitted by the alternativeenergy source modules 104 over the AC power line cable 108. In theillustrative embodiment, the demodulation circuit 150 may include anamplifier 152, that may receive a sensor signal from a current sensor140 coupled to the AC power line cable 108. The amplifier 152 mayamplify and condition the sensor signal, which may be provided to ademodulator 154. The demodulator 154 may demodulate information from thesensor signal and provide the demodulated information to a processor156, which may subsequently save the information in local or remote datastorage, transmit the information to a remote device (e.g., a remotemonitor computer), generate local or remote alarms (via an alarm circuit159), or take some other action in response to the information. Theprocessor 156 may be embodied as any type of processor capable ofperforming the functions described herein including, but not limited to,a microprocessor, digital signal processor, microcontroller, or thelike. Depending on the type of modulation used by the alternative energysource modules 104, the demodulation circuit 150 may include ananalog-to-digital converter (designated “ADC”) 158 in addition to, or inplace of, the demodulator 154. Regardless, each of the demodulators 154and the analog-to-digital converters 158 are configured to supply thedemodulated information to the processor 156. As will become moreapparent, the inverter array gateway 112 can selectively enable ordisable the alternative energy source modules 104, organize measureddata therefrom into data structures (e.g., position tables), andcommunicate the resulting tables remotely (via a wired or wirelessconnection) to, without limitation, a mobile phone or a computer of auser.

In some embodiments, the system 100 may also include a maintenance tool160, which may be utilized by an installer or repairer of thealternative energy source modules 104. Similar to the inverter arraygateway 112, the maintenance tool 160 is configured to communicate withthe alternative energy source modules 104. However, when the maintenancetool 160 is coupled to the AC power line cable 108, a switch 164 of theservice panel 110 may be opened to decouple the array 102 from the powergrid. In such embodiments, the alternative energy source modules 104 maydiscontinue generation of AC output power (e.g., by detecting anislanding condition). As such, the maintenance tool 160 and thealternative energy source modules 104 may utilize the AC power linecable 108 solely for communication purposes (i.e., not for delivery ofpower as normal) while the array 102 is disconnected from the powergrid. In such circumstances, a communication protocol of higherbandwidth, relative to communication techniques using the AC power linecable 108 while AC output power is begin supplied, may be used (e.g., aModbus protocol). The maintenance tool 160 may include a communicationcircuit 162 to support such “off-line” communications with thealternative energy source modules 104. As illustrated, the maintenancetool 160 may be located within or outside of the inverter array gateway112.

Turning now to FIG. 2, illustrated is a simplified block diagram of anembodiment of an inverter 122 of the system 100 of FIG. 1. In thesimplified block diagram illustrated in FIG. 2, the inverter circuit 124of the inverter 122 may include an input converter 200 electricallycoupled to a DC bus 204 and an output converter 202 with an inputelectrically coupled to the DC bus 204. Additionally, in someembodiments, the inverter circuit 124 may also include an input filter210 electrically coupled to the input converter 200 and the DCphotovoltaic module 120 and an output filter 212 electrically coupled tothe output converter 202 and the service panel 110.

In the illustrative embodiment, the input converter 200 may be embodiedas a DC-to-DC converter configured to convert low voltage DC power tohigh voltage DC power. That is, the input converter 200 converts the DCpower received from the DC photovoltaic module 120 to a high level DCvoltage power, which is supplied to the DC bus 204. The output converter202 may be embodied as a DC-to-AC converter configured to convert thehigh voltage DC power from the DC bus 204 to AC power, which is suppliedto the service panel 110, and thereby the power grid at the gridfrequency.

The inverter controller 126 may be electrically coupled to the inputconverter 200 and configured to control the operation of the inputconverter 200 to convert the low voltage DC power received from the DCphotovoltaic module 120 to the high voltage DC power supplied to the DCbus 204. Additionally, in some embodiments, the inverter controller 126may control the operation of the input converter 200 based on a maximumpower point tracking (“MPPT”) algorithm or methodology. To do so, theinverter controller 126 may provide a plurality of control signals tovarious circuits of the input converter 200.

The inverter controller 126 may also be electrically coupled to theoutput converter 202 and configured to control operation of the outputconverter 202 to convert the DC power of the DC bus 204 to AC powersuitable for delivery to the power grid via the service panel 110.Additionally, as discussed in more detail below, the inverter controller126 may be configured to control the operation of the output converter202 so as to provide a test signal via an output waveform of theinverter circuit 124. In particular, the inverter controller 126 maygenerate switch signals to control the operation of a plurality ofswitches of the output converter 202 to provide a test current (acontribution current) to the power grid via the service panel 110.

Turning now to FIGS. 3 and 4, illustrated are simplified circuitdiagrams of an embodiment of the inverter circuit 124 of FIG. 2.Beginning with FIG. 3, the input converter 200 may include an invertercircuit 300, a transformer 302, and a rectifier circuit 304. Theinverter circuit 300 may be embodied as a DC-to-AC inverter circuitconfigured to convert the DC waveform supplied by the DC photovoltaicmodule 120, via the input filter 210, to an AC waveform delivered to aprimary winding 360 of the transformer 302. For example, the invertercircuit 300 may be illustratively embodied as a bridge circuit formed bya plurality of switches 350, 352, 354, 356. Each of the switches 350,352, 354, 356 may be configured to receive a corresponding controlsignal q_(IC1), q_(IC2), q_(IC3), q_(IC4), from the inverter controller126 (illustrated in FIG. 2) to control an operation of the invertercircuit 300. The inverter controller 126 may use pulse-width modulation(“PWM”) to control the switches 350, 352, 354, 356 at a relatively highswitching frequency (e.g., at a frequency such as, without limitation,100 kilohertz (“kHz”) that is substantially higher than the AC gridfrequency, which is typically 50 or 60 hertz (“Hz”)). As discussedabove, the input converter 200 converts the DC waveform from the DCphotovoltaic module 120 to a first AC waveform based on control signalsreceived from the inverter controller 126. In the illustrativeembodiment, the inverter circuit 300 may be embodied as a full-bridgecircuit, but other circuit topologies such as a half-bridge circuit maybe used in other embodiments. Additionally, although each of theswitches 350, 352, 354, 356 is illustrated as metal-oxide semiconductorfiled-effect transistor (“MOSFET”) devices, other types of switches canbe used in other embodiments.

The transformer 302 may be embodied as a two or more winding transformerhaving the primary winding 360 electrically coupled to the invertercircuit 300 and a secondary winding 362 coupled to the rectifier circuit304. The transformer 302 may be configured to convert the first ACwaveform supplied by the inverter circuit 300 at the primary winding 360to a second AC waveform at the secondary winding 362. The first andsecond AC waveforms may have substantially equal frequencies and may ormay not have substantially equal voltages. The illustrative transformer302 includes the primary winding 360 electrically coupled to theinverter circuit 300 and the secondary winding 362 electrically coupledto the rectifier circuit 304. The transformer 302 may provide galvanicisolation between the primary side circuitry (including DC photovoltaicmodule 120) and the secondary side circuitry (including the DC bus 204).The turns ratio of the transformer 302 may also provide voltage andcurrent transformation between the first AC waveform at the primarywinding 360 and the second AC waveform at the secondary winding 362.

The rectifier circuit 304 may be electrically coupled to the secondarywinding 362 of the transformer 302 and configured to rectify the secondAC waveform to a DC waveform supplied to the DC bus 204. In theillustrative embodiment, the rectifier circuit 304 may be embodied as afull-bridge rectifier formed from a plurality of diodes 370, 372, 374,376. Again, in other embodiments, other circuit topologies and othercomponents such as synchronous rectifiers may be used in the rectifiercircuit 304.

The DC bus 204 may be coupled to the rectifier circuit 304 of the inputconverter 200 and to the output converter 202. The DC bus 204 may beconfigured to store energy from the input converter 200 and transferenergy to the output converter 202 as needed. To do so, the DC bus 204may be maintained at a high voltage DC value relative to DC voltagevalues produced by the DC photovoltaic module 120 and may include a DCbus capacitor 380. The particular value of capacitance of the DC buscapacitor 380 is dependent on the particular parameters of the invertercircuit 124 such as the desired voltage level of the DC bus 204, theexpected requirements of the power grid, and/or the like.

As shown in FIG. 4, the output converter 202 may be electrically coupledto the DC bus 204 and configured to convert the DC bus waveform to theoutput AC waveform, which is filtered by the output filter 212. Theoutput converter 202 may include a DC-to-AC inverter circuit 400configured to convert the DC waveform supplied by the DC bus 204 to anAC waveform delivered to the output filter 212. For example, theinverter circuit 400 may illustratively be embodied as a bridge circuitformed by a plurality of switches 402, 404, 406, 408. Each of theswitches 402, 404, 406, 408 may be configured to receive a correspondingcontrol signal q_(OC1), q_(OC2), q_(OC3), q_(OC4), from the invertercontroller 126 to control operation of the output converter 202. Asdiscussed above, the inverter controller 126 may use PWM to control theswitches 402, 404, 406, 408 to generate a pulse width modulated ACwaveform. Again, it should be appreciated that although the illustrativeoutput converter 202 is embodied as a full-bridge circuit, other circuittopologies such as a half-bridge circuit may be used in otherembodiments. Additionally, although each of the switches 402, 404, 406,408 is illustrated as a MOSFET device, other types of switches may beused in other embodiments.

The input filter 210 and output filter 212 may be configured to providefiltering functions of the DC input waveform from the DC photovoltaicmodule 120 and the AC output waveform to the power grid, respectively.The input filter 210 illustratively includes a filtering capacitor 390and a filtering inductor 392. However, other filtering components andtopologies may be used in other embodiments. The output filter 212 maybe configured to filter the output voltage by reducing the conductedinterference and satisfying regulatory requirements. In the illustrativeembodiment, the output filter 212 may include differential-modeinductors 420, 422, a line filter capacitor 424, and common-modeinductors 426, 428. Again, however, other filtering component andtopologies may be used in other embodiments.

Turning now to FIG. 5, illustrated is a simplified block diagram of anembodiment of the inverter controller 126 of the inverter 122 of FIG. 2.The inverter controller 126 may include various control modules tocontrol the operation of the input converter 200 and the outputconverter 202. With specific regard to the control of the outputconverter 202, the inverter controller 126 may include processingcircuitry 500 and output sense circuitry 502, which provides varioussensed signals to the processing circuitry 500. The processing circuitry500 may be embodied in, or otherwise include, the processor 130 and/orthe memory 132 of the inverter controller 126 (see FIG. 1), as well asadditional circuitry and/or devices. The output sense circuitry 502 mayinclude a plurality of sensing circuits to sense various currents andvoltages of the inverter 122 and/or power grid. In the illustrativeembodiment, the output sense circuitry 502 may be configured to sense orcalculate the local power grid line voltage V_(LINE) _(_) _(RMS), thelocal grid phase (or phase angle of the local grid voltage) θ_(LINE),and the output power P_(OUT) associated with the inverter 122. However,in other embodiments, additional or other currents, voltages, and/orcircuit characteristics may be sensed or otherwise measured by theoutput sense circuitry 502.

The processing circuitry 500 may include a plurality of control modules,which may be embodied as firmware/software programs (e.g., stored in thememory 132), discrete hardware circuitry, and/or a combination ofhardware and software. In the illustrative embodiment, the processingcircuitry 500 may include an output current controller 510 and an outputconverter control module 512. Of course, it should be appreciated thatadditional or other modules, functionality, and features may be includedin the processing circuitry 500 depending on the particularimplementation. Additionally, it should be appreciated that although theoutput current controller 510 and the output converter control module512 are illustrated in FIG. 5 as separate modules, the functionality ofany one or more thereof may be incorporated into another module of theprocessing circuitry 500.

The output current controller 510 may be configured to generate commandsignals as a function of a plurality of other signals and/orcharacteristics of the inverter 122. For example, in the illustrativeembodiment, the output current controller 510 may generate a currentcommand signal i_(OC)* as a function of a bus voltage V_(BUS) (see FIG.3) of the DC power bus 204, the local power grid line voltage V_(LINE)_(_) _(RMS), and the local grid phase θ_(LINE). Of course, in otherembodiments, the output current controller 510 may generate the currentcommand signal i_(OC)* based on additional or other signals of theinverter 122. Additionally, although the command signal may be embodiedas a current command signal i_(OC)* in FIG. 5, the command signal may beembodied as a voltage command signal, a duty cycle command signal, oranother type of command signal in other embodiments.

The output converter control module 512 may be configured to control theoperation of the output converter 202. To do so, the output convertercontrol module 512 may be configured to generate the control signalsq_(OC1), q_(OC2), q_(OC3), q_(OC4) that control the operation of theswitches 402, 404, 406, 408 of the output converter 202. In theillustrative embodiment, the output converter control module 512 mayinclude a proportional-integral module (designated “PI”) 520 configuredto generate a duty cycle command signal d_(OC) based on the currentcommand signal i_(OC)* and a feedback signal of an output current i_(OC)of the inverter 122. The duty cycle command signal d_(OC) may beprovided to a pulse width modulation control module (designated “PWM”)522, which generates the control signals q_(OC1), q_(OC2), q_(OC3),q_(OC4) based on the duty cycle command signal d_(OC). The outputconverter control module 512 may also include a pulse mode controlmodule 530 configured to generate the control signals q_(OC1), q_(OC2),q_(OC3), q_(OC4) that control the operation of the switches 402, 404,406, 408 when the output converter 202 operates in a pulse mode ofoperation. For a better understanding of an operation associated withthe pulse mode control module 530, see U.S. Pat. No. 8,284,574 entitled“Method and Apparatus for Controlling an Inverter using Pulse ModeControl,” to Chapman, et al., issued Oct. 9, 2012, which is incorporatedherein by reference. The output converter control module 512 may alsoperform various safety and/or quality verification checks on theinverter 122 such as ensuring that the output power remains within anacceptable range, protecting against anti-islanding conditions, and/orother functions.

Turning now to FIG. 6, illustrated is a simplified block diagram of anembodiment of a branch circuit (or an array) 600 including a pluralityof alternative energy source modules 604, numbered consecutively from 1to N, that are connected via cable impedances 601, also numberedconsecutively from Z₁ to Z_(N). The cable impedances 601 are depicted asresistances, but one of ordinary skill in the art would understand thatthe cable impedances 601 could also include inductances andcapacitances. However, at the frequency of a power grid 610, which isapproximately 60 Hz in the United States, resistances would likelydominate the impedances. The power grid 610 provides a grid voltageVgrid and may include grid interconnection equipment such as a servicepanel, a disconnect switch, surge protection, and power meters. Thealternative energy source modules 604 may also contain module impedances602. The module impedances 602 are typically very high at 60 Hz, beingmuch larger than the cable impedances 601, and are typically dominatedby the capacitances of “X capacitors” and/or “Y capacitors,” which areoften used to reduce conducted emissions that may produceelectromagnetic interference.

Each alternative energy source module 604 may provide a contributioncurrent 603, also designated i₁ to i_(N), to a cable network includingthe cable impedances 601. The contribution currents 603 sum to provide abranch current (designated “i_(branch)”) 605. The contribution currents603 and the branch current 605 are typically alternating currents thatmay or may not have a phase shift relative to the grid voltage Vgrid ofthe power grid 610. However, according to standards such as IEEE 1547,which is incorporated herein by reference, the power factor of eachalternative energy source module 604 may be unity, meaning that thecontribution currents 603 (and therefore the branch current 605) are inphase with the grid voltage Vgrid of the power grid 610. As such,reading FIG. 6 from left to right, the peak or root mean square (“RMS”)values of the contribution currents 603 may be simply additive andaccumulate as follows. The leftmost cable impedance 601 would conductonly i_(N). The next-to-leftmost cable impedance 601 would conducti_(N)+i_(N−1). Likewise, the third-from-leftmost cable impedance 601would conduct i_(N)+i_(N−1)+i_(N−2), and so on.

Each cable impedance 601 in combination with its conducted current maycontribute a voltage drop according to Ohm's Law. The alternative energysource modules 604 may have corresponding terminal voltages 606, alsoreferred to as V1 through VN (wherein V1 and VN refer to terminalvoltages for the first and Nth alternative energy source modules 604,respectively). For example, the terminal voltage V1 can be calculated asV1=Vgrid+(i₁+i₂+ . . . +i_(N))·Z₁. Assuming the contribution currents603 are positive or zero (that is, in phase with the grid voltageVgrid), the terminal voltage V1 may be greater than or equal to the gridvoltage Vgrid of the power grid 610. Likewise, the terminal voltage V2can be calculated as V2=V1+(i₂+i₃+ . . . +i_(N)) Z₂, wherein V2, i₂ andZ₂ represent a terminal voltage, a contribution current and a cableimpedance, respectively, of a second alternative energy source module604. As such, the terminal voltages relate according to V2≧V1. Likewise,all the terminal voltages V1 through VN may be similarly calculated andthe terminal voltages relate according to VN≧VN−1≧ . . . ≧V1≧Vgrid. Assuch, the relative terminal voltages V1 through VN can be used toindicate the relative position of a particular alternative energy sourcemodule 604 in the branch circuit 600.

Note that the cable impedances 601 may or may not be equal, although insystems connected with prefabricated cables, the impedances Z₂ throughZ_(N) may be approximately equal. In that case, the impedance Z₁ mayinclude the prefabricated cable impedance as well as the impedance ofpotentially lengthy wires that connect the branch circuit 600 to thepower grid 610. This potentially lengthy connection is sometimesreferred to as a “whip cable.” As such, the impedance Z₁ is not only thehighest impedance, but it also conducts the full branch current 605 and,therefore, has the largest voltage drop.

Turning now to FIG. 7 illustrated is a graphical representation of anembodiment of a distribution of the terminal voltages 606 in the branchcircuit 605 of FIG. 6. The plot of a monotonic order of the terminalvoltages 606 (designated “Module Voltage” in volts, root mean square(“V”, RMS”)) versus the position (designated “Module Number/Position”)of the alternative energy source modules 604 assumes that the impedancesZ₂ through Z_(N) are five milliohms (“mΩ”), the impedance Z₁ is 50 mΩ,the grid voltage Vgrid is 240 Vrms, and the contribution current 603 ofeach alternative energy source module 604 is one ampere.

As apparent from FIG. 7, the terminal voltages 606 measured by, forinstance, an inverter controller (see, e.g., the inverter controller 126of FIG. 5) may be compared to infer the relative position of thealternative energy source modules 604 in the branch circuit 600.However, the contribution currents 603 from each alternative energysource module 604 are unlikely to be equal and, therefore, the actualplot of the terminal voltages 606 versus position in the branch circuit600 will generally not be as smooth as that shown in FIG. 7. Theterminal voltages 606 should, nonetheless, be monotonically increasingwith position.

More generally, one can conduct a circuit analysis to determine that therelationship of the terminal voltages 606 to the contribution currents603 and the cable impedances 601 can be expressed as a matrix equationv=Zi+[1 1 1 . . . 1]^(T) Vrms. In this equation, “v” is a vector of theterminal voltages 606, “i” is a vector of the contribution currents 603,and Z is a matrix of impedances (e.g., cable impedances 601). Duringnormal operation, the alternative energy source modules 604 may producethe contribution currents 603 in response to their available power(e.g., from sunlight) and in response to conditions of the power grid610. The alternative energy source modules 604, however, can be placedinto a characterization mode via commands from the inverter arraygateway (see, e.g., the inverter array gateway 112 of FIG. 1). In thecharacterization mode, for example, the inverter array gateway mayspecify that a subset (perhaps just one) of alternative energy sourcesmodules 604 is enabled while the remaining alternative energy sourcemodules 604 are disabled. In doing so, for instance, the output currentcontroller 510 of the inverter controller 126 (see FIG. 5) may enablethe output current control of the subset of alternative energy sourcemodules 604 and disable the output current control of the remainingalternative energy source modules 604.

In such a situation, some or all of the contribution currents 603 in thevector i may be zero. If only one contribution current 603 is enabled(or injected), then variation in the vector v may solely be due to thatone contribution current 603. More specifically, if a contributioncurrent IM for an Mth alternative energy sources module 604 is enabled(1<M<N), then one would expect to see a distribution of voltage rises inthe terminal voltages 606 that are numbered V1 through VM and nearly aconstant voltage in the terminal voltages 606 that are numbered VM+1through VN. Indeed, one would expect that VM=VM+1=VM+2= . . . =VN sincethere would be substantially no current flowing in the cable impedances601 beyond VM.

Note that the inverter controller 126 of each alternative energy sourcemodule 604 may be equipped with the output current controller thatsenses the local power grid line voltage V_(LINE) _(_) _(RMS) at itsoutput terminals, which is substantially equal to the terminal voltage606 for a given alternative energy source module 604. Via an inverterarray gateway 112, the alternative energy source modules 604 can reporttheir measurements of the local power grid line voltage V_(LINE) _(_)_(RMS) such that inverter array gateway becomes aware of all theterminal voltages 606. Likewise, each alternative energy source module604 may also report other metrics such as its output power, thecontribution current 603, serial number, and fault codes, if any.

By enabling one alternative energy source module 604 and collectingmeasurements of all the terminal voltages 606, the inverter arraygateway 112 can sort the terminal voltages 606 and create a first listfrom least to greatest in a data structure such as a sorted positiontable. The inverter array gateway 112 can also sort the change in theterminal voltages 606 and create a first from least to greatest in thesorted position table. By looking at the changes rather than theabsolute measurements, the inverter array gateway 112 may reduce (e.g.,minimize) the effect of scaling errors due to tolerance of themeasurement circuits of the alternative energy source modules 604. Sucha first list from least to greatest of the sorted position table mayserve as a proxy for the positions of the alternative energy sourcemodules 604 in the branch circuit 600. It should be understood that thedata structure may be embodied in other representations such as a map orgraph in addition to the table discussed herein to delineate a relativeposition of the alternative energy source modules 604.

As noted above, if only one contribution current 603 is enabled, thensome terminal voltages 606 may be substantially equal, meaning they arelocated “upstream” from the enabled contribution current 603. This meansthat in the first list from least to greatest, it is uncertain where toplace such alternative energy source module 604. To further ascertainthe positions of the alternative energy source modules 604 havingsubstantially equal terminal voltages 606, one can repeat the aboveprocess for a different contribution current 603 by first disabling allalternative energy source modules 604 then enabling a contributioncurrent 603 of one of the alternative energy source modules 604, whichwe will label module P, that is not in the first “M” modules from thefirst list from least to greatest. Likewise, a second list from least togreatest can be formed such that alternative energy source modules 604numbered 1 through P should show a distribution of terminal voltages 606and alternative energy source modules 604 P+1 through N should show asubstantially equal terminal voltage 606. This process can be repeatedas many times as necessary until a final list from least to greatest ofthe sorted position table has been obtained in which all the terminalvoltages 606 1 through N are distributed and not substantially equal.This final list from least to greatest of the sorted position tablerepresents the relative positions of alternative energy source modules604 within the branch circuit 600.

The voltage measurements of the terminal voltages 606 are generallyprone to some measurement error. Since the difference between any twoterminal voltages 606 may be small, measurement error can cause thesorting to be inaccurate. One source of error is simply precision anddrift in voltage sensors. Another source of error is that the terminalvoltages 606 could be sampled at different times.

One way to correct for sensor error is to have the inverter arraygateway 112 disable all the alternative energy source modules 604 and tosample all the terminal voltages 606. In this circumstance, all theterminal voltages 606 should be substantially equal as there should beno significant current flowing in the cable impedances 601. Thesedisabled-state measurements of the terminal voltages 606 can bere-scaled or otherwise re-calibrated such that they are allsubstantially equal. These scaling factors may be recorded and appliedto future measurements of the terminal voltages 606.

Differences in sampling times of the terminal voltages 606 can occur dueto serial communications that occur between the alternative energysource modules 604 and the inverter array gateway 112. That is, theinverter array gateway 112 may “poll” the alternative energy sourcemodules 604 during a polling cycle. If the alternative energy sourcemodules 604 report their most recent sampling of the terminal voltages606, they may be reporting voltages that are seconds or minutes apart intime. One way to counteract this may be to configure the inverter arraygateway 112 and the alternative energy source modules 604 with a “snap”command. The snap command may be issued from the inverter array gateway112 and broadcast to all of the alternative energy source modules 604.Upon receiving the snap command, each alternative energy storage module604 may immediately sample its terminal voltage 606 and store it forlater download. At a later time, the inverter array gateway 112 may thenpoll the alternative energy source modules 604 and recall the snappedvoltage measurements of the terminal voltages 606. In this way, theterminal voltages 606 may be sampled at approximately the same time.

Turning now to FIGS. 8 and 9, illustrated are simplified flow diagramsof embodiments of methods for mapping relative positions of a pluralityof alternative energy source modules. While the methods may be performedby an inverter array gateway, other equipment that has access to thearray or to the inverter array gateway may perform the method 800 aswell. Additionally, ones of the aforementioned steps of the respectivemethods may be omitted or re-ordered, or other steps may be addeddepending on the application therefor. Beginning with FIG. 8, the method800 commences by entering a characterization mode in a step or module801 followed by disabling the alternative energy source modules in astep or module 802. Then, the terminal (or module) voltages for thealternative energy source modules are sampled in a step or module 803,optionally using the snap technique described above. At this point, thesampled terminal voltages would ideally be equal, but due to measurementand timing errors the terminal voltages will generally only beapproximately equal.

Therefore, in a step or module 804 the sampled terminal voltages areused to calculate correction factors. Then, a loop is entered wherein analternative energy source module (designated “X”) is enabled one at atime in a step or module 805. The terminal voltages are sampled in astep or module 806 and corrected, in a step or module 807, by applying ascaling/correction factor. After the correction, the terminal voltagesare sorted into a data structure such as a position table from least togreatest in a step or module 808. This table forms the basis of thealternative energy source module position within a branch circuit (see,e.g., the branch circuit 600 of FIG. 6). In a decisional step or module809, a determination is made whether the terminal voltages of thealternative energy source modules show a distribution throughout thebranch circuit. For instance, does the distribution indicate that thealternative energy source module X is last in the branch circuit. If so,then the method records the final sorted position table for thealternative energy source modules in the branch circuit in a step ormodule 810 and the method 800 concludes. If not, then in a step ormodule 811, the alternative energy source module X is changed to adifferent value that is chosen among the non-distributed terminalvoltages and the method 800 returns to the step or module 805.

Turning now to FIG. 9, the method for mapping relative positions of aplurality of alternative energy source modules begins at a start step ormodule 900. The method continues by injecting a first contributioncurrent (e.g., the contribution current 603 described with respect toFIG. 6) into a power grid by a first alternative energy source module ofthe plurality of alternative energy source modules at a step or module905. The method continues with determining an output voltage (e.g., theterminal voltage 606 described with respect to FIG. 6) for ones of oreach of the plurality of alternative energy source modules for instance,substantially simultaneously, at a step or module 910.

The first alternative energy source module can modulate an outputvoltage waveform coupled to the power grid to report the output voltagefor the first alternative energy source module. The first alternativeenergy source module can also modulate an output voltage waveformcoupled to the power grid to report at least one of an output power, aserial number, a fault code and the first contribution current for thefirst alternative energy source module.

The method then constructs a data structure such as a sorted positiontable of the relative positions of the plurality of alternative energysource modules employing the output voltage for ones of or each of theplurality of alternative energy source modules in accordance with, forinstance, the graphical representation of FIG. 7, in a step or module915. An inverter array gateway (such as the inverter array gateway 112introduced in FIG. 1) in communication with of the plurality ofalternative energy source modules may construct the sorted positiontable. The sorted position table can provide a monotonic order of theoutput voltage for ones of or each of the plurality of alternativeenergy source modules. The sorted position table can be constructed byemploying a change in the output voltage for ones of or each of theplurality of alternative energy source modules. The sorted positiontable may include positioning a second alternative energy source moduleof the plurality of alternative energy source modules upstream of thefirst alternative energy source module when the output voltage of thefirst alternative energy source module is substantially equal to theoutput voltage of the second alternative energy source module.

In a decisional step or module 920, the method determines if the sortedposition table is complete. If the sorted position table is notcomplete, the method continues with disabling the first contributioncurrent in a step or module 925 and injecting a second contributioncurrent into the power grid by a second alternative energy source moduleof the plurality of alternative energy source modules in a step ormodule 930. In a step or module 935, the method determines anotheroutput voltage for ones of or each of the plurality of alternativeenergy source modules, and then constructs another sorted position tableof the relative positions of the plurality of alternative energy sourcemodules employing the another output voltage for ones of or each of theplurality of alternative energy source modules in a step or module 940.

Thereafter, or if the sorted position table is complete pursuant to thedecisional step or module 920 above, the method determines if the arrayincluding the plurality of alternative energy source modules should becalibrated in a decisional step or module 945. If the array should becalibrated, the method continues by disabling the plurality ofalternative energy source modules and calibrating the output voltage forthe plurality of alternative energy source modules in a step or module950. It should be noted that the calibration step can also be performedat other times within the process and often at the beginning to ensurethat the plurality of alternative energy source modules are calibratedbefore mapping the relative positions thereof. Then, it is determined ifthe method should be repeated in a step or module 955. If the methodshould be repeated, the method returns to the step or module 905 tostart over again. If the array should not be calibrated and the methodshould not be repeated pursuant to the decisional steps or modules 945,955, respectively, the method is complete in an end step or module 960.It should be noted, that the method may also include detecting a failureby observing changes over time of an impedance matrix representingconductors coupling the plurality of alternative energy source modulesto the power grid at any time or throughout the process described above.

Turning now to FIG. 10, illustrated is a simplified block diagram of anembodiment of a plurality of branch circuits 1010 forming a multi-brancharray 1000. The multi-branch array 1000 of a plurality of branchcircuits 1010 may be connected to a power grid 1020. The connections topower grid 1020 may occur via conductors such as whip cables 1030. Notethat each whip cable 1030 may include a plurality of conductors (such asline 1, line 2, ground, and neutral for split-phase 240 VAC, 60-Hz powergrids). The whip cables 1030 are often threaded through conduit from arooftop to a service panel. The whip cables 1030 may include a portionof the rightmost cable impedance 601 discussed with respect to FIG. 6.Each branch circuit 1010 may effectively be connected in parallel to thepower grid 1020 via ends of the whip cables 1030 and are fed with thesame voltage.

The methods discussed above can be extended to the multi-branch array1000. With reference to FIG. 6, a single branch circuit 600 may benecessarily limited by the current rating of the circuit breakers andwires involved. For example, a 20 ampere (“A”) circuit breaker connectedto the 240 volts alternating current (“VAC”), split-phase system may belimited to 80 percent of (20 A)(240 V) of power capability, per the U.S.National Electric Code. If each alternative energy source module 604 israted for 240 watts (“W”), this limits each branch circuit 600 to 16alternative energy source modules 604 that can individually providecontribution currents 603 up to one ampere each.

One of ordinary skill in the art would recognize that the approach canbe extended to a plurality of branch circuits 1010 connected to the samepower grid 1020. In the case of the plurality of branch circuits 1010,when a single alternative energy source module is enabled, the terminalvoltages of only one branch circuit 1010 may increase. All terminalvoltages not exhibiting voltage rise would be considered inhabitants ofother branch circuits 1010 and can be discarded from the sorting of afirst sorted position table. One need only repeat the methods for eachbranch circuit 1010 to fill in the sorted position tables therefor.

After obtaining the data structure such as the sorted position tablesfor all the branch circuits 1010, the data may be used to automaticallypopulate a graphical user interface depicting the alternative energysource modules along with their serial numbers or other availableinformation. The graphical user interface may be accessible from theinverter array gateway via the Internet or via direct connection theretousing a wired connection such as “Cat-5” cable, serial communicationssuch as RS-485, and/or local wireless communications such as “Bluetooth”or “WiFi.” For example, one may access the graphical user interface witha mobile phone or tablet computer via Bluetooth connections to inspectthe populated array layout. Typically, through this graphical userinterface, one would be able to reposition the depictions of thealternative energy source modules so that they visually line up with aknown actual or desired orientation. In any case, the connectionsbetween the depictions of the alternative energy source modules arepreserved per the data of the sorted position tables.

In addition to the automated array mapping method described above,further characterization of an array is possible via analysis of themeasured terminal voltages. The impedance matrix Z discussed above canbe calculated by utilizing power data, branch current data, and terminalvoltage data. Furthermore, if it is known that at least some cableimpedances are the result of prefabricated cables, then those cableimpedances can be known in advance of installation. The determination ofthe impedance matrix Z, or specific elements thereof, can be doneperiodically to determine if changes are occurring in the array. Suchchanges could be indicative of failures of alternative energy sourcemodules, loose connections, and the like. Information pertaining to theimpedance matrix Z could be use advantageously to those conductingmaintenance or repairs on the array by aiding them in isolating problemsspecific to some alternative energy source modules or some cableimpedances. Such an analysis can be done remotely via the Internet orlocally using a maintenance tool.

As a further aid in array characterization, module impedances (e.g.,module impedance 602 of FIG. 6) may also be favorably utilized. In acondition wherein all alternative energy source modules are disabled,branch circuit and/or array impedances may be dominated by the relativehigh module impedances. Since the module impedances can be known inadvance by the manufacturer, a measurement of the branch circuitimpedance may be indicative of the total count of the alternative energysource modules connected to a power grid. For example, if a singlemodule impedance is ten kilo-ohms at a given frequency, then if thereare 20 alternative energy source modules in the array, one would expectto measure a total impedance of approximately 500 ohms since theimpedances are approximately in parallel (neglecting the small cableimpedances). If the measured impedance differs significantly from 500ohms, in this example, then one would expect that there may be a failedconnection or a failed alternative energy source module in the branchcircuit. A maintenance tool may be used to provide test signals to thearray or to one or more branch circuits to make the array impedancedetermination. Thus, the collective module impedances for a branchcircuit or array may be measured via an inverter array gateway ormaintenance tool, and based on the collective module impedancemeasurement a determination is made whether the array has a failure.

Thus, a system including an array of a plurality of alternative energysource modules (see, e.g., the array 102 of the plurality of alternativeenergy source modules 104 of FIG. 1) and an inverter array gateway (see,e.g., the inverter array gateway 112 of FIG. 1) has been introducedherein. In one embodiment, a first alternative energy source module maybe configured to inject a first contribution current (e.g., thecontribution current 603 described with respect to FIG. 6) into a powergrid (e.g., the power grid 610 of FIG. 6) and determine an outputvoltage (e.g., the terminal voltage 606 described with respect to FIG.6) resulting therefrom. The first alternative energy source module maybe configured to determine the output voltage thereof in response to acommand to the plurality of alternative energy source modules from theinverter array gateway. The first alternative energy source module mayfurther be configured to modulate an output voltage waveform coupled tothe power grid to report the output voltage for the first alternativeenergy source module. The first alternative energy source module mayfurther be configured to modulate an output voltage waveform coupled tothe power grid to report at least one of an output power, a serialnumber, a fault code or the first contribution current for the firstalternative energy source module.

The inverter array gateway may be configured to receive an outputvoltage for ones of or each of the plurality of alternative energysource modules, and construct a data structure such as a sorted positiontable of relative positions of the plurality of alternative energysource modules employing the output voltage for ones of or each of theplurality of alternative energy source modules in accordance with, forinstance, the graphical representation of FIG. 7. The inverter arraygateway may be configured to construct the sorted position table byproviding a monotonic order of the output voltage for ones of or each ofthe plurality of alternative energy source modules. The inverter arraygateway may also be configured to construct the sorted position table byemploying a change in the output voltage for ones of or each of theplurality of alternative energy source modules. The inverter arraygateway may also be configured to construct the sorted position table byidentifying a position of a second alternative energy source module ofthe plurality of alternative energy source modules upstream of the firstalternative energy source module when the output voltage of the firstalternative energy source module is substantially equal to the outputvoltage of the second alternative energy source module.

Under certain circumstances, the system may perform a second iterationto map relative positions of the plurality of alternative energy sourcemodules. Thus, the first alternative energy source module may beconfigured to disable the first contribution current and a secondalternative energy source module of the plurality of alternative energysource modules is configured to inject a second contribution currentinto the power grid and determine another output voltage resultingtherefrom. The inverter array gateway may be configured to receiveanother output voltage for ones of or each of the plurality ofalternative energy source modules and construct another sorted positiontable of the relative positions of the plurality of alternative energysource modules employing the another output voltage for ones of or eachof the plurality of alternative energy source modules.

At any time in the process, the system can calibrate the plurality ofalternative energy source modules by disabling the plurality ofalternative energy source modules, and calibrating the output voltagefor the plurality of alternative energy source modules. In view of faultanalysis, the inverter array may also be configured to detect a failureby observing changes over time of an impedance matrix representingconductors coupling the plurality of alternative energy source modulesto the power grid.

As provided herein, technologies for characterizing certain aspects ofan array of alternative energy source modules are disclosed. Thetechnologies may include determining the relative position of thealternative energy source modules in the array and characterizations ofthe module electrical network of the array. The technologies may alsoinclude utilizing the characterizations to diagnose failure or improperinstallation conditions. The technologies may further include providingdata of the relative positions and characterizations to a user via aninverter array gateway that may communicate wirelessly or as wired withother computing devices or maintenance tools.

For a better understanding of power supplies, see “Modern DC-to-DCSwitchmode Power Converter Circuits,” by Rudolph P. Severns and GordonBloom, Van Nostrand Reinhold Company, New York, N.Y. (1985) and“Principles of Power Electronics,” by J. G. Kassakian, M. F. Schlecht,and G. C. Verghese, Addison-Wesley (1991). The aforementioned referencesare incorporated herein by reference in their entirety.

Also, although the present embodiments and advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the claims. For example, many of the processesdiscussed above can be implemented in different methodologies andreplaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, claims on embodiments are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

The invention claimed is:
 1. A method for mapping relative positions ofa plurality of alternative energy source modules, comprising: injectingonly a first contribution current into a power grid by a firstalternative energy source module of said plurality of alternative energysource modules; determining an output voltage for each of said pluralityof alternative energy source modules; and constructing a data structureindicative of said relative positions of said plurality of alternativeenergy source modules employing said output voltage for ones of saidplurality of alternative energy source modules.
 2. The method as recitedin claim 1, further comprising: disabling said first contributioncurrent; injecting a second contribution current into said power grid bya second alternative energy source module of said plurality ofalternative energy source modules; determining another output voltagefor each of said plurality of alternative energy source modules; andconstructing another data structure of said relative positions of saidplurality of alternative energy source modules employing said anotheroutput voltage for ones of said plurality of alternative energy sourcemodules.
 3. The method as recited in claim 1 wherein said firstalternative energy source module modulates an output voltage waveformcoupled to said power grid to report said output voltage for said firstalternative energy source module.
 4. The method as recited in claim 1wherein said first alternative energy source module modulates an outputvoltage waveform coupled to said power grid to report at least one of anoutput power, a serial number, a fault code or said first contributioncurrent for said first alternative energy source module.
 5. The methodas recited in claim 1 wherein said constructing said data structureemploys a change in said output voltage for ones of said plurality ofalternative energy source modules.
 6. The method as recited in claim 1wherein said constructing said data structure comprises positioning asecond alternative energy source module of said plurality of alternativeenergy source modules upstream of said first alternative energy sourcemodule when said output voltage of said first alternative energy sourcemodule is substantially equal to said output voltage of said secondalternative energy source module.
 7. The method as recited in claim 1wherein said constructing said data structure provides a monotonic orderof said output voltage for ones of said plurality of alternative energysource modules.
 8. The method as recited in claim 1, further comprising:disabling said plurality of alternative energy source modules; andcalibrating said output voltage for said plurality of alternative energysource modules.
 9. The method as recited in claim 1 wherein saiddetermining said output voltage for each of said plurality ofalternative energy source modules occurs substantially simultaneously.10. The method as recited in claim 1, further comprising detecting afailure by observing changes over time of an impedance matrixrepresenting conductors coupling said plurality of alternative energysource modules to said power grid.
 11. A system, comprising: an array ofa plurality of alternative energy source modules including a firstalternative energy source module configured to inject only a firstcontribution current into a power grid and determine an output voltageresulting therefrom; and an inverter array gateway configured to:receive an output voltage for each of said plurality of alternativeenergy source modules, and construct a data structure of relativepositions of said plurality of alternative energy source modulesemploying said output voltage for ones of said plurality of alternativeenergy source modules.
 12. The system as recited in claim 11 whereinsaid first alternative energy source module is configured to disablesaid first contribution current and a second alternative energy sourcemodule of said plurality of alternative energy source modules isconfigured to inject a second contribution current into said power gridand determine another output voltage resulting therefrom, said inverterarray gateway being configured to receive another output voltage forones of said plurality of alternative energy source modules andconstruct another data structure of said relative positions of saidplurality of alternative energy source modules employing said anotheroutput voltage for ones of said plurality of alternative energy sourcemodules.
 13. The system as recited in claim 11 wherein said firstalternative energy source module is further configured to modulate anoutput voltage waveform coupled to said power grid to report said outputvoltage for said first alternative energy source module.
 14. The systemas recited in claim 11 wherein said first alternative energy sourcemodule is further configured to modulate an output voltage waveformcoupled to said power grid to report at least one of an output power, aserial number, a fault code or said first contribution current for saidfirst alternative energy source module.
 15. The system as recited inclaim 11 wherein said inverter array gateway is configured to constructsaid data structure by employing a change in said output voltage forones of said plurality of alternative energy source modules.
 16. Thesystem as recited in claim 11 wherein said inverter array gateway isconfigured to construct said data structure by identifying a position ofa second alternative energy source module of said plurality ofalternative energy source modules upstream of said first alternativeenergy source module when said output voltage of said first alternativeenergy source module is substantially equal to said output voltage ofsaid second alternative energy source module.
 17. The system as recitedin claim 11 wherein said inverter array gateway is configured toconstruct said data structure by providing a monotonic order of saidoutput voltage for ones of said plurality of alternative energy sourcemodules.
 18. The system as recited in claim 11 wherein said inverterarray gateway is further configured to: disable said plurality ofalternative energy source modules; and calibrate said output voltage forsaid plurality of alternative energy source modules.
 19. The system asrecited in claim 11 wherein said first alternative energy source moduleis configured to determine said output voltage thereof in response to acommand to said plurality of alternative energy source modules from saidinverter array gateway.
 20. The array as recited in claim 11 whereinsaid inverter array gateway is further configured to detect a failure byobserving changes over time of an impedance matrix representingconductors coupling said plurality of alternative energy source modulesto said power grid.